In work apparatus such as brushcutters, edge cutters or the like, a relatively long guide tube is provided between the drive motor and its housing, on the one hand, and the driven rotatable work tool on the other hand. The guide tube accommodates the drive shaft. With this arrangement, a relatively soft connection is presented between the motor and the work tool. During operation, vibration problems can result in connection with the interaction between the drive motor and the driven work tool.
The guide tube is connected to the motor housing via an anti-vibration element in order to avoid such vibration problems. The occurring vibration problems must be effectively damped by such an anti-vibration element. At the same time, a reliable connection of the guide tube to the motor housing must be provided thereby.
Configurations are known wherein a clamp is fixed with clamping lugs on the motor end of the guide tube. The clamp has clamping lugs, for example, made of plastic or die cast metal. A tubular-shaped damping element made of elastic material is pushed over the clamp. For assembly, the unit comprising the guide tube with the clamp and the damping element is pressed into a corresponding receptacle of the motor housing. The clamping lugs project at the end face beyond the motor housing which requires a correspondingly large amount of space for accommodating the same. The press-in operation requires complex devices and alignment errors in the assembly state cannot be precluded. An exchange of the guide tube, for example, at a service station is difficult without corresponding devices. A guide tube seated with precision during manufacture can become displaced or rotate relative to the motor housing under high or continuous loads. The clamping action between the clamp and the guide tube can deteriorate when the material yields, for example, in the case where the clamp is made of plastic. For an embodiment wherein the clamp is made of die cast aluminum, the clamp is very stiff so that it can adapt to the guide tube only to a limited extent.
It is an object of the invention to provide a vibration-dampening connection of a guide tube to the housing of a work apparatus as well as to improve the exchangeability of a guide tube.
The portable handheld work apparatus of the invention includes a brushcutter and an edge cutter. The portable handheld work apparatus includes: a housing; a guide tube having first and second ends; a drive shaft rotatably journalled in the guide tube; a rotatable work tool mounted at the second end of the guide tube; a drive motor mounted in the housing for rotatably driving the work tool via the drive shaft; an anti-vibration unit for holding the guide tube in the housing at the first end of the guide tube; the anti-vibration unit including a clamp surrounding the guide tube; an elastic damping element disposed between the housing and the clamp; and, the clamp and the housing being configured for fixing the clamp form tight in the housing.
For the above, the clamp, which surrounds the guide tube, is fixed form-tight to the housing of the motor. This affords the possibility to omit pressing the damping element into the motor housing under high pretension. With the form-tight connection, the assembly comprising the guide tube and the anti-vibration unit is reliably fixed on the housing and is secured against rotation or displacement. A rotation or displacement of the guide tube relative to the clamp is permanently avoided by the excellent clamping action between the two. A simple exchange without special tools is possible because of the configuration of the form-tight connection. The form-tight fixation of the clamp on the motor housing is practical in the region where the clamp for the guide tube is secured with threaded fasteners.
It is advantageous when the clamp is configured as an approximately cylindrical clamping sleeve having one or several longitudinal slots and two or more clamping lugs which can be clamped against each other and which extend radially outwardly and are arranged laterally of the longitudinal slot. The housing has an end face at the end thereof facing toward the guide tube and further has a cutout in the end portion in which the clamping lugs of the clamp are accommodated. At the same time, a reliable clamping of the clamp on the guide tube is provided with the clamping lugs with simple means. The clamping lugs project radially and lie in the cutout of the housing and simultaneously also form a form-tight configuration to prevent rotation. The rotation is here prevented without additional devices. The cutout at the end of the housing is advantageously open in the direction of the end face so that the clamping lug can be inserted into the receptacle from the end face for assembly without disassembly of the housing.
In a practical embodiment, the clamping lugs each include a bore for passing through a clamping bolt for which at least one and preferably two openings are provided in the housing for accommodating the ends of the clamping bolt. These openings are aligned approximately coaxial to the clamping bolt. In this way, after assembly of the clamp, the clamping bolt can be guided through one of the two openings in the housing as well as through the corresponding bores in the clamping lugs and then be clamped, that is, threadably tightened. The two ends of the clamping bolt, which lie in the openings of the housing, are then held in a form-tight manner and additionally form also a form-tight connection to ensure against an axial displacement which is in addition to the above-described form-tight security against rotation.
A part of the elastic damping element is advantageously configured in the form of damping bushings surrounding the ends of the clamping bolt. In this way, an effective damping of vibrations in the peripheral and longitudinal directions with respect to the guide tube is given with simple means directly at the form-tight connection of the clamp to the motor housing. The damping bushings advantageously include a peripheral collar with which they are form-tightly fixed in the housing. In this way, they are easy to assemble and protected against dropping out when loosening the clamping bolt. It is practical to arrange the damping bushings so that the clamping lugs of the clamp lie tightly against the end face of the damping bushing and especially against the end face of the collar of the bushing. With this arrangement, no force-transmitting intermediate elements are needed. In addition to an excellent damping action, a relatively rigid connection of the guide tube to the housing is provided.
In a simple and practical configuration, the clamping bolt is configured as a threaded bolt having a head and a nut. A first metal sleeve for accommodating the head is provided in one bushing and a second metal sleeve for accommodating the nut is provided in the other bushing. The metal sleeves are especially made of steel. The steel sleeves can be manufactured in a simple and cost-effective manner and prevent an excessive areal pressing between the clamping bolt and the damping bushings.
In an advantageous embodiment, the sleeves include two flats lying approximately parallel to each other between which the nut is held against rotation. As a consequence thereof, the clamping bolt, which is configured as a threaded bolt, need only be rotated at its head with a suitable tool without it being necessary to hold the nut with a further tool. An arrangement of this kind simplifies the automatization of manufacture as well as the exchange of a damaged guide tube or the anti-vibration unit as may be required.
In a further practical embodiment, the sleeve and the nut can be configured also as one piece whereby the number of parts to be assembled is reduced. The sleeves have a holding slot on the end face thereof into which a screwdriver can be seated as needed. For example, in the case of a thread which has become fixed because of rust, the screw connection of the clamping bolt can be loosened without this being made more difficult by a rotation of the sleeve. It is practical to provide an ensurance against rotation on the sleeve and this can be especially in the form of a hexagon formed thereon. Such an ensurance against rotation is held in the elastic damping sleeve or in a hexagonally-shaped cutout of the clamp whereby the occurring torque is taken up during the assembly of the bolt.
In an advantageous variation, a set nut is pressed into the sleeve. In this way, a fix against rotation is provided by the form-tight connection of a serrated, milled or knurled collar of the set nut.
The clamping sleeve is advantageously surrounded by a damping sleeve as a further part of the anti-vibration unit and of the corresponding damping element. The damping sleeve lies in the corresponding receptacle of the housing for the guide tube. In this way, in addition to the rotation and longitudinal vibration damping, an effective damping against bending vibrations is provided. It is practical when the damping sleeve has a cutout which surrounds the clamping lugs of the clamp. The clamping action between the clamp and the guide tube occurs in the region of the clamping lugs. For this reason, there is here a transfer of force from the guide tube via the clamp in the region of the clamping lugs and via the damping sleeve directly into the motor housing in this region. With an arrangement of this kind, an excellent damping action as well as a relatively rigid and therefore precise connection of the guide tube to the housing can be achieved. For simplifying assembly, the damping sleeve has a lug which projects radially outwardly and this lug projects into the cutout of the housing for accommodating the clamping lugs whereby a rotation of the damping sleeve is prevented.
In an advantageous embodiment, the clamping sleeve is extended in the direction of the motor beyond the region of the clamping lugs. In this region, the clamping action is low but with the extended configuration, a secure guidance of the guide tube during assembly and also during operation is provided. The longitudinal slot extends between the two clamping lugs advantageously over the entire length of the clamping sleeve whereby the assembly is considerably simplified. In this way, the possibility is especially provided to first seat the damping sleeve and thereafter the clamping sleeve in the motor housing in that the clamping sleeve is pressed together at the two clamping lugs and is pushed into position. Thereafter, for example, with a screwdriver or even in an automated operation, the longitudinal slot can be expanded against the spring force of the damping sleeve so that the guide tube can be pushed into the clamping sleeve without developing force.
The clamp is advantageously manufactured as a single piece and is especially made of sheet metal. In addition to a cost-effective manufacture, a reliable clamping of the guide tube is also given thereby because, on the one hand, the sheet metal can adapt to a certain extent to the guide tube and, on the other hand, the developed clamping force can be maintained permanently because of the absence of creep behavior in the material. The clamping lugs are advantageously provided with reinforcing creases whereby, on the one hand, the sheet metal of the clamping lugs can be configured so thin that a desired adaptation to the guide tube can be achieved. On the other hand, the clamping lugs are sufficiently reinforced by the reinforcement creases so that the lugs do not yield because of the development of a clamping force by the clamping bolt.
The damping elements and especially the damping bushings as well as the damping sleeve preferably have a set of slots on the interior side and on the exterior side. Because of these longitudinal slots, the deformability of the elastic damping material is ensured also in the assembled state because the elastic material can deviate under load in the direction of the slots. To support this effect, the set of longitudinal slots on the interior side and the set of longitudinal slots on the exterior side are offset relative to each other in the peripheral direction.
The elastic damping elements are preferably of adapted stiffness. The particular stiffness of the damping sleeve and of the damping bushings can be adapted independently of each other whereby the possibility is provided to optimally dampen the various longitudinal, rotational and bending modes of vibration. Here, the selection of adapted Shore hardness has been shown to be especially practical.